Current gas turbine engines are used in a variety of applications including the powering of aircraft, marine craft, electrical generators, and pumps, among others. Generally, the gas turbine engine is designed or constructed to operate most efficiently in a predetermined compressor flow pressure ratio range and predetermined turbine flow pressure ratio range, the ranges being selected for so called "balanced operation" between the turbine and the compressor. Such balanced flow pressure ratios are determined from the intended engine application and the engine power output range for such application.
Because such an engine does not always operate at a single power output, the balance between the compressor and turbine can be expanded over a broader range through use of mechanically variable geometry engine components such as variable inlet vanes, variable fan blades, variable compressor blading, variable exhaust nozzles, etc, in selected combinations. Such mechanically variable components are modulated by engine controls during operation to affect certain engine operating parameters in a preselected manner under different operating conditions. However, such mechanically variable components in the high temperature operating turbine portion of the engine can be difficult and costly to construct and maintain.